If he has not taken all the assessments for the qualification it is unlikely that the exam board will certificate (or finalise) the AS Grade until he does. If both the AS (and A2 which I assume he will also be doing next year) qualifications are listed on UCAS as 'pending' he should be okay. However, to be fair, his application would be stronger if he already had the full AS while going through the process. If there is a good reason why he did not have the time to do the assessment it may be worth a very small mention in his personal statement.